CH. LV.] THE LAKYNGOSCOPE 755 



fibres which pass into the aryteno-epiglottidean fold may assist in depressing the 

 epiglottis. 



If these muscles are paralysed, the lips of the glottis are no longer parallel, but 

 are curved with the concavity inwards, and a much stronger blast of air is required 

 for the production of the voice. 



5. Arytenoid. When the mucous membrane is removed from the back of the 

 arytenoid cartilages, a band of transverse fibres is exposed, on the dorsal surface of 

 which are two slender decussating oblique bundles. These are often described as 

 separate muscles (arytenoid and aryteno-epiglottidean), but they are intimately 

 blended together. The ventral fibres (arytenoid proper) pass straight across from 

 the outer half of the concave surface on the back of one arytenoid cartilage to the 

 corresponding surface of the other. The dorsal fibres can be followed to the lateral 

 walls of the larynx, the uppermost ones to the cartilage of Santorini, the intermediate 

 ones run with the uppermost fibres of the thyro-arytenoid muscle forming the so- 

 called aryteno-epiglottidean muscle, and the lowest fibres blend at the level of the 

 true vocal cords with the thyro-arytenoid and lateral crico-arytenoid muscles. 



The arytenoid muscle draws the arytenoid cartilages together. If it is paralysed, 

 the intercartilaginous part of the glottis remains open, although the membranous lips 

 can still be "approximated during vocalisation. 



It has been generally supposed that the epiglottis is depressed as a lid over the 

 glottis during swallowing. This may be so in some animals, but in man it is not 

 the case ; the epiglottis projects upwards in close contact with the base of the tongue. 

 The necessary closure of the glottis during swallowing is brought about by the con- 

 traction of the arytenoid and thyro-arytenoid muscles ; by this means the arytenoid 

 cartilages are drawn towards each other, and also forwards into contact with the 

 posterior surface of the epiglottis (Anderson Stuart). Henle remarks that "the 

 muscles which lie in the space enclosed by the laminae of the thyroid cartilage and 

 above the cricoid may be regarded in their totality as a kind of sphincter such as is 

 found in its simplest form embracing the entrance of the larynx in reptiles " (Quain's 

 Anatomy). 



Nerves. The larynx is supplied by two branches of the vagus ; the superior 

 larynyeal is the sensory nerve; by its external branch, it supplies one muscle, 

 namely, the crico-thyroid. These fibres, however, probably arise from glosso- 

 pharyngeal rootlets (see p. 645). The rest of the muscles are supplied by the 

 inferior laryngeal nerve, the fibres of which come from the spinal accessory, not 

 the vagus proper. 



The laryngoscope is an instrument employed in investigating during life the 

 condition of the pharynx, larynx, and trachea. It consists of a large concave mirror 

 with perforated centre, and of a smaller mirror fixed in a long handle. The patient 

 is placed in a chair, a good light (argand burner, or electric lamp) is arranged on one 

 side of, and a little above, his head. The operator fixes the large mirror round his 

 head in such a manner, that he looks through the central aperture with one eye. 

 He then seats himself opposite the patient, and so alters the position of the mirror, 

 which is for this purpose provided with a ball-and-socket joint, that a beam of light 

 is reflected on the lips of the patient. 



The patient is now directed to throw his head slightly backwards, and to open his 

 mouth ; the reflection from the mirror lights up the cavity of the mouth, and by a 

 little alteration of the distance between the operator and the patient the point at 

 which the greatest amount of light is reflected by the mirror in other words, its 

 focal length is readily discovered. The small mirror fixed in the handle is then 

 warmed, either by holding it over the lamp, or by putting it into a vessel of warm 

 water ; this is necessary to prevent the condensation of breath upon its surface. 

 The degree of heat is regulated by applying the back of the mirror to the hand or 

 cheek, when it should feel warm without being painful. 



After these preliminaries the patient is directed to put out his tongue, which is 

 held by the left hand gently but firmly against the lower teeth by means of a 

 handkerchief. The warm mirror is passed to the back of the mouth, until it rests 

 upon and slightly raises the base of the uvula, and at the same time the light is 

 directed upon it : an inverted image of the larynx and trachea will be seen in the 

 mirror. If the dorsum of the tongue is alone seen, the handle of the mirror must 



